chapter_02 student_SP07_1 - Chapter 2: Atoms and the Atomic...

Chapter 2: Atoms and the Atomic Theory CHM 25 Spring 2007 Contents 2-1 Early Chemical Discoveries and the Atomic Theory 2-2 Electrons and Other Discoveries in Atomic Physics 2-3 The Nuclear Atom 2-4 Chemical Elements 2-5 Atomic Mass 2-6 Introduction to the Periodic Table 2-7 The Concept of the Mole and the Avogadro Constant 2-8 Using the Mole Concept in Calculations Early Discoveries and the Atomic Theory Lavoisier 1774 -Law of Conservation of Mass • Disproved the “phlogiston theory” by studying the thermal decomposition of mercury calx. Mercury Calx + heat Mercury + a Gas •Saw that the mass before and after stayed constant, either direction of the reaction. •Named the gas “Oxygen” •Named the metal calx “Metal Oxides”

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Law of Conservation of Mass The total mass of substances present after a chemical reaction is the same as the total mass of substances before the reaction. Simply stated : Matter is neither created nor destroyed during a chemical reaction. This concept will come into play in Studio #3 when we look at the decomposition of metal carbonates. Conservation of Mass Early Discoveries and the Atomic Theory Proust 1799 -Law of Constant Composition •Studied copper carbonate, the two tin oxides, and the two iron sulfides to prove this law. •He did this by making artificial copper carbonate and comparing it to natural copper carbonate. •With this he showed that each had the same proportion of weights between the three elements involved (Cu, C, O).

Law of Constant Proportions • Sometimes referred to as: Law of Definite Proportions No matter what its source, a particular compound is composed of the same elements in the same parts (fractions) by mass. • Mass % : obtained by dividing the mass of each element by the total mass of the compound. Early Discoveries and the Atomic Theory Dalton 1803-1888 – Atomic Theory Using the two fundamental laws given above he proposed the Atomic Theory. 1. Each chemical element is composed of minute, indivisible particles called atoms. Atoms can neither be created, nor destroyed during a chemical reaction. 2. All atoms of an element are alike in mass (weight) & other properties, but atoms of one element are different from those of all other elements. 3. In each of their compounds, different elements combine in a simple numerical ratio. Consequences of Dalton’s theory Law of Definite Proportions: combinations of elements are in ratios of small whole numbers. ± Mass 72.7 % O 27.3 % C Mass 57.1 % O 42.9 % C Neither d = 1.98 g/L d = 1.25 g/L Carbon Oxide II Carbon Oxide I

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Law of Definite Proportions Formula: CO 2 (Carbon Dioxide) Formula: CO (Carbon Monoxide) Carbon Oxide II Carbon Oxide I The characteristic relative masses of the atoms of the various elements became known as atomic weights.

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